The present invention relates generally to superconductivity, and more particularly relates to a method of manufacturing superconducting magnesium diboride objects.
The recent discovery of superconductivity in magnesium diboride (MgB2) having a superconducting transition temperature (Tc) of approximately thirty nine degrees Kelvin (39 K) introduced a new, simple binary intermetallic superconductor having three atoms per formula unit. MgB2 has a Tc that is higher by almost a factor of two of any known non-oxide and non-C60-based compound. Measurements of the boron isotope effect in MgB2, which is an indication of the extent to which phonons mediate superconductivity, are consistent with the superconductivity being mediated via electron-photon coupling. Measurements of the upper critical field, Hc2(T), the thermodynamic critical field, Hc(T), and the critical current, Jc, indicate that MgB2 is a type-II superconductor with properties that are consistent with an intermetallic superconductor that has a Tc of approximately 40 K.
It is believed that MgB2 forms via a process of diffusion of magnesium (Mg) vapor into boron grains. Superconducting wire, tape, and film can be used for research and applied purposes. For example, superconducting wire can be used for making superconducting magnets, fault-current limiters, and for power transmission. Films can be used to make Josephson junctions, SQUIDS (superconducting quantum interference devices), micro-electronic interconnects and other devices. The films can also be used to coat microwave cavities and other objects.
It is an object of the instant invention to provide a method of manufacturing magnesium diboride wires, tapes, and films. It is a further object of the instant invention to provide a method of manufacturing magnesium diboride wire using boron filaments and films using boron films.
In view of the above objects, it is an object of the instant invention to provide a method of manufacturing magnesium diboride wire and films utilizing simple cost effective techniques.
In accordance with an embodiment of the instant invention, a method of manufacturing magnesium diboride wire or film comprises the steps of exposing boron filaments, tape, or film to Mg vapor for a predetermined time and temperature to form MgB2 wire, tape or film, removing the formed MgB2 wire, tape or film from the Mg vapor, and either quenching the MgB2 wire, tape or film to near ambient temperatures or quenching the reaction vessel to near ambient temperatures and removing the MgB2 wire, tape or film from the reaction vessel.
In accordance with an alternate embodiment of the instant invention, a method of manufacturing magnesium diboride wire, tape or film comprises the steps of: a) sealing at least one boron filament, tape or film and magnesium into a tantalum (Ta) or similarly inert tube with excess magnesium with respect to MgB2; b) protecting the tantalum from oxidation (e.g., sealing the Ta tube in quartz); c) heating the sealed Ta tube at 950 C. for two hours or less for a boron filament diameter of 100 micrometers (with differing heating times and temperatures for differing thicknesses of boron used); d) quenching the Ta tube to room temperature and removing the formed magnesium diboride wire, tape or film from the Ta tube.
Other objectives and advantages of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.